I
`
`'
`
`'
`
`.
`
`‘
`
`——-——
`
`Volume 14 Number 6 August 1998
`
`379—380 B riefReviews
`J. S. Graln’nsmin
`
`
`Original A rticles
`181—384 INFLIIENCE OF THE REFERENCE CA8 OF PAHIMACNETIC
`OHTIIEII HNALTZEHS O" NITROGEN CONCENTHNTIONS
`IIIIIIIHO CLOSED-CIRCUIT INESTHESIO
`jan F. A. Hrndrirhx, MD, Audra/1.]. iJanZnnih'ri. M'D,
`
`PhD, and Aiidi'i' M. rh' fal/hif, MD
`
`385—391 H'MILIIOILITY OF HECOHOS IN MI OIITI’ATIEIIT
`PIIEMIESTHETIC EONLIINTION CLINIC
`Carrion L, Cihini, MD, and I’Viihcm K. Schwah, PhD
`393—402 I” WHO EIIIILIHITIIIII OF II CLOSE” LOOP MONITORING
`STIIATEIIT FOH IIIIIIICEO PHHIILTSIS
`
`Dccpah Ramakrishna, 1148, Khamuu Brhhchani, PhD, PE.
`Kevin Kicia. M D, jqfih’ y ha‘ahhmr. M S,
`H’oif 14/. van i‘u/Iahzahn, PhD, PE, Raier C. Ehrrharr, PhD,
`and Michaci Daiiar, i143
`
`403—412 HEELECTANCE PULSE OXIMETIIY— PRINCIPLES MIC
`CSTETHIC IPFLICHTION IN THE ZIIIIICH “STEIN
`
`Vaihrr Kc'inig, Renate Hnrh, and Aihm Hath
`413—420 ACCURACY OF IJOLIIME MENSOHEMENTS IN MECHANICAL”
`VENTILNTEII NEWBOHNS:
`ABBII‘II'AIIATWE STIIB‘I IIF enmmsncm nemcas
`Kai Raske, Bern'am Faiiziie, Raiami R. I/Vrmcl', and
`Gerri Schmaiisrh
`
`
`421—424 N" EVOLUTIONARY SOLUTION TO ANESTHESIR NUTOHITEO
`HECOIIO KEEPING
`
`Algorithm
`44i—446 II HEM-TIME ALGORITHM TO II'I'II’HOIIE THE RESPONSE TIME
`OF A CLINICIIL MlllTlCilS NNHLTSEII
`Lawriy Wong, MSc, Rnih Hamihon. MB. ChB,
`
`Eiin'n Paiayinm, PhD. and Clive Hahn, D. Phii
`
`.rl
`
`_Cage, MD, and
`Ahn'n A. Bide”, Ph D, John
`
`Pani}. Poppers, M D
`EHHLOHTION OF A PITCT TTPE SPIHOMETEH IN HELIIIIIT/
`OXTOEN MIXTOHES
`Saran Suadei'qaard. MD, Signrbm'gnr Ka'msan. M D,
`
`Srqfaa Lumiin, MT), and Oh: Simqvisf, M'D
`433—459 OETECTIOH OF “INC INJUHT WITH CONVENTIONAL MIC
`HEOHHL NETWORK-BOSE" OHNLI'SIS OF CONTINUOUS [IOTA
`
`jnhha Rast‘incn, MD, and Mauricio A. Lean, MD
`
`Book: Review
`447 L. C. HENSON AND A. C. LEE [EDS]: SIMOLNTOHS IN
`ANESTHESIOLOOY EOIICHTION
`Richard Mani:
`
`
`
`449—450 INFORMATION FOR ICONTHIIIOTOIIS
`
`\
`‘
`*
`
`KLIJWEII nonnemc PunusnEns
`2—5:‘Efiia—iHNAinfifififififl'EREW"m"
`IN ANAESTHESIA nun INTENSIVE cane, ANII or
`THE SOCIETY FOR TECHNOLOGY IN ANESTNESIA
`
`wiser
`
`=
`
`~
`
`1-
`
`' :21
`
`JUL 30 1999
`JOHN ‘
`-.
`.
`
`ow
`Apple Inc.
`
`w. .. ..
`
`US Patent NO' 8=989=83OCODEN JCMOEH
`ISSN 1337—1307
`
`I
`
`Apple Inc.
`APL1014
`U.S. Patent No. 8,989,830
`
`FITBIT, Ex. 1014
`
`

`

`Volume 14 Number6 August 1998
`
`JOURNAL OF OLINIOAI. MONITORING
`AND OONIPUTINO
`FFIOIAI. JOURNAL OF THE EUROPEAN SOCIETY FOII COMPUTING AND TEOHNOLOOI" IN ANAESTIIESIA ANIl INTENSIVE BANE [ESOTAIIII
`NO OF THE SOEIET‘I FOB TEOHNOLOEY IN ANESTIIESIA [STA]
`
`M B
`
`Harvey L.‘ Edmonds. MD
`John H. Eichhom. Ml)
`TammyY. Euliauo, MD
`M. Fisher, MD
`A. Dean Forbes
`
`llflhedr'iir
`
`11
`
`Wolfgang Friesdorf. MD
`Yasuhiro Fukui. PhD
`Leslie ch des. PhD
`Nikolaus Gravenstein, MD
`A. Gerson Greenburg, MD, PhD
`G. l-ledensticrna, MD
`Wolfgang Heinrichs, MD
`R. C. G. Gallandat Huet, MD
`Kazuyuki Ikeda, MD
`Ville Jantti. MD
`Gavin N. C. Kenny. MD
`Samsun Lampotang, PhD
`j.W. R. McIntyre. MD
`James H. Philip, MD
`Michael L. Quinn, PhD
`Pradccp Ramaaya, MD
`Ira]. Rampil, MD
`Gunter Rau. MD
`Michael F. Roizen. MD
`].—A. Remand, MD
`William B. Rnnciman, MD
`Keith Ruskin, MD
`David A. Sainshury, MD
`H. Schillings, MD
`John W. Severinghaus. MD
`M. Michael Shabot, MD
`Dean Forrest Sittig, l’hl)
`Bradley E. Smith, MD
`Richard Tcplick. MD
`Kevin K. Tremper, MD
`jorge Urzua, MD. PhD
`Karel H. Wesseling, PhD
`Dwayne Westcnskow. PhD
`j. C. Wyatt. PhD
`
`TIIE PARENT JUU IINAlS
`lttm'tmtianttiJorn'nnl of Clinical Alut-tit‘ot‘ittg and Computing,
`founded by Omar Prakash in 1984; Reed Gardner, senior
`editor; and the
`tlrl'mtitort‘t-tg, Founded in 1985 by N.‘i"y
`Jianrntttl' qf Clinical
`Smith, Allen K. Ream. and]. S. Gravenstein.
`'
`
`EUITOIIS
`jefi'tcy M. Feldman. MD
`Allegheny University Hospitals. MCP
`Dept. ofAnesthesiology
`3300 Henry Avenue
`Philadelphia, PA19129, U.S.A.
`E—mail: Feldmalij@al.lhs.cdu
`
`J. S. Gravenstein, MD, Coordinating Editor
`UF/College ochdicine
`Dept. ofAnesthesiology
`P.O. Box100254
`Gainesville, FL 32610. U.S.A.
`E-mail: jgravens@ancst2.anest.ufi.edi|
`Ilkka Kalli, MD, PhD
`City Maternity Hospital
`Dept. of Anaesthesiology
`P.O. Box 61
`FIN-00971 Helsinki, Finland
`E~mailz ilkka.kalli@iki.Fi
`Publisher
`Kluwcr Academic Publishers
`9.0. Box 990
`3300 AZ. Dordrecht,The Netherlands
`E-mail: Locs.Wils@ wkap.nl
`
`EUITONIAI. NANII
`Paul G. Barash, MD
`' Gerard Bashcin. MD, PhD
`Charlotte Bell, MD
`Jan E.W. Benekcn, PhD
`J. A. Elem. PhD
`]. G. Bovill. MD. PhD
`Peter Carstcn sen
`William P. Coleman. PhD
`jefl'rey E. Cooper, PhD
`John Doyle. MD
`Ronald Dueck. MD
`Peter C. Duke. MD
`
`ISSN 1387-1307
`
`All rights reserved
`© 1998 Kluwer Academic Publishers
`No part of the material protected by this copyright notice may be
`reproduced or utilised in any form or by any means. electronic or
`mechanical. including photocopying. recording or by any informa—
`tion storage and retrieval system. without written permission from
`the copyright owner.
`
`Printed in the Netherlands
`
`Printed on «drifter paper
`
`JUL 3 O 1999
`June Cl I-
`6m IIFBHLAHU at
`
`S “M”?
`‘immbuw. wt
`._.
`..
`
`‘IIOLUIIIE I4. 8 ISSUES. IOOO
`Issues include:
`Brief Reviews, Editorials. Clinical Articles. Research Ar-
`ticles. Educational Articles. Book Reviews, Correspondence,
`Selections from the Anesthesia Patient Safety Foundation
`Newsletter.
`
`KittmerAmrit-ntic Pnln'isltrts. Dordrecht. Boston. London
`
`Kluwer Academic Publishers Online
`Visit our website at http; H www.wkap.nl
`
`Thcjrnrrnrti of Clinical tlvltlniwring and Computing is indexed in index
`Mrtlt‘rtts. Cum-tn Contents/Clinical Medicine. Ermnntt llaiedim, Current
`Atlmrt'rtt'ss in Biological Scienrrs. and the Biomedical Engineeriigg Citation
`Index. and is indcxedfabsu'acted in Engineering Index, Srirntt' Citation
`Index. Expanded Resenrrt't Alt-t1, Marika Documentation Service.
`
`II
`
`FITBIT, Ex. 1014
`
`

`

`
`
`I This material may be protected by Copyright law [Title 1? us. Code]
`
`
`
`
`BEFLEBTflNBE PULSE UXIMETIW— PRINCIPLES Mill]
`DBSTETHIG APPLIBATIUN IN THE ZUHIEH SYSTEM
`
`Milli-cht'ii-iiq, Renate Hitch, mid/illicit Hl'ffil
`
`From the Perinatal Physiology Research Department. Department
`of Obstetrics, Zurich University Hospital. CH—Stlfll Zurich. Switzer—
`land.
`
`Received Nov I3, 1997, and in revised formjun 23. 1998, Accepted
`for publication Aug 4,1998.
`
`Address correspondence to Volkcr Kiinig, Perinatal Physiology Re—
`search Department. Department of Obstetrics Zurich University
`Hospital. Cl-LRU‘JI Zurich. Switzerland
`E-mail: vkgt'ct fhk.usz.ch
`
`Jonrimiquii'm'm.‘ .iriuam'mn'ng and Continuing 14: 403-412. 1998.
`I998 Kliirilci'zlrmietirir Publishers. Pri'nicil'i'n lilt' a\-'t'tlit'rlmrds.
`
`sors — and a sensitive modern pulse oximctcr. However,
`
`Kiinig V. lluirh R. Huch A. Reflectance pulse oxilnetry — principles
`and obstetric application in the zurich system.
`J Clin Monit 1998: 14:40:57412
`ABSTBAGT. Transmission and reflectance are the two main
`
`modes ofpulsc oximetry. 1n obstetrics. due to the absence ofa
`transilltnninabie fetal part for transmission oxinietry. the only
`feasible option is the reflectance mode, in which sensor and
`detector are located on the same surface of the bod}J part.
`[-lowever. none of the reflectance pulse oxiineters developed
`for intrapartum use are fully satisfactory, as indicated by the
`fact that none have entered routine use. We have designed,
`developed, constructed and tested a reflectance pulse oxiineter
`with the possibility to adjust the electronic circuits and Signal
`processing in order to determine the effects of various para ni~
`eters on signal amplitude and wave—form and to optimize the
`sensitivity and spatial arrangement ofthe optical elements.
`Following an explanation of the principles of reflectance
`pulse oxiinetry, we report our experience with the design,
`development, construction and field-testing of an in—housc
`reflectance pulse oximctry system for obstetric application.
`
`KEY WEEDS. Oxygen saturation, reflectance pulse oximetry,
`intraparttun feta] monitoring.
`
`INTRIJDIIBTIIIN
`
`l’ulsc oximctry is the combination of spectrophotome—
`try and plethysmography. It permits rapid noninvasive
`measurement of arterial oxygen saturation with the
`added advantages ofsiniple sensor application and direct
`measurement, requiring neither calibration not pre-
`adjustincnt. Pulse oxiinetcts are thus in widespread and
`fast—increasing use. e.g. in intensive care, anesthetics and
`neonatology [1]. All these applications employ “trans—
`mission” pulse oximetry, so called because the light
`used to determine blood oxygen saturation is “trans-
`mitted" from a light emitter on one side of the body
`part to a light receiver on the other side; suitable sites
`are the fingers in adults or hands and feet in neonates or
`children, which are said to be “transilluminated.”
`in obstetrics, fetal oxygen status during labor is a
`crucial parameter. However, no transiliuminablc fetal
`part is available. The only option in this case is reflec—
`tance oximeti'y [2], using a sensor with its light emisi
`sion and detection elements on the same surface of
`
`the body part. Various types of such a reflectance pulse
`oximctcr have been developed for intrapartum use at
`various locations. However, fora wide variety of reasons,
`all are still experimental and not in full routine use [3—7].
`Basically a reflectance measurement can be achieved
`using planar sensors — which can he produced, for
`example. by modifying conventional transmission sen-
`
`403
`
`FITBIT, Ex. 1014
`
`

`

`404 jom'iminfCiinimliid'onfmriirqmid Comparing Vm‘H N06 Augiisri998
`
`PBINBII’LES [IF PIILSEIIXIMETIIY
`
`Signal recording
`
`Light is absorbed on passing through matter. The de-
`gree of absorption depends on the nature of the trans-
`illuminated material and the wavelength of the light
`employed. All optical techniques for determining arte—
`rial oxygen saturation use the marked difference in the
`absorption of red light between oxygenated and re—
`duced hemoglobin.
`The absorption of light passing through bone or
`noupulsatile tissue is constant over time. Oxygenated
`and reduced hemoglobin in the arterial vascular bed, on
`the other hand, cause changes in absorption timed by
`the heart rate due to the pulsatile variation in artery
`thickness. The total intensity of the light after passing
`through tissue can be measured, for example, as the
`photocurrent 1(t) ofa photodiode, and is obtained from
`the Lambert—Beer absorption law as:
`
`I“) = I“ ' exp(_5tisslle ' 5)
`' CXP(_(QO2 ' EHIJO +
`(1— so» - an «ion
`
`5i
`H
`
`dc 1 DC : Iiissur + Idir
`
`where
`
`intensity ofincident light
`In
`slim”: mean absorption coefficient oftissue (function of
`wavelength)
`mean thickness oftrausilluminated tissue
`
`.
`
`30;
`
`oxygen saturation to be determined (: HbO}
`(HbO + Hb), i.e. ratio of oxygenated hemoglo-
`bin concentration to sum of oxygenated and
`reduced hemoglobin concentrations)
`absorption coefficient of oxygenated hemoglobin
`(function of wavelength)
`
`and a signal which varies in time with the pulsatile
`change in artery thickness
`
`AC 3 1mm- ' (502 ' EI-ibo + {l — 502) '5Hb) ' dit)
`
`{4)
`
`with amplitude
`
`ac = l(diastole) — [(systole) =
`
`llissue '
`
`' EHhO + (I — 502) ' EHli) ' d‘
`
`at“,
`
`d(t)
`
`absorption coeflicient of reduced hemoglobin
`(function of wavelength)
`time function of mean pulsatile change in artery
`thickness, with amplitude d = d(diastolc) —
`d (systole)
`
`Measurement may be impaired by light transmitted
`directly from the light source to the receiver or light
`which does not pass through arterially perfused tissue.
`Ifthis "direct light” 1,“, is taken into account, Equation
`(1) changes to:
`
`1(t) 2 [tissue ‘ CXP(*(303 ' E‘Hbo-i-
`(I — SOzi'EHbl‘d(tll+1dir
`
`(“l
`
`where
`
`Ilissul: : It! ' expi—Elissn‘c ' 5)
`
`Since the pulsatile component of the absorption is at
`most a few percent, i.e. the exponent of the second e
`function in Equation (1) is very small, we can use the
`approximation:
`
`expfx) = l +x for
`
`(<1
`
`to obtain the very close approximation:
`
`lit) 2
`[tissue ‘ (1 — {502 ' EHho + l1 — 502) ‘ Eula ' ‘13)) + Idir
`
`(lb)
`
`This light intensity is measured in the photodiodes and
`can be broken down electronically into two compo»
`nents, a time—independent signal
`
`DC 2 Ilissut‘ + Idir
`
`with amplitude equal to the value ofthis signal
`
`(2)
`
`(3)
`
`such instruments come with a “black—box” microproces—
`sor—controlled mode ofoperation making constructional
`adjustments to the electronic circuits and signal process~
`ing virtually impossible. As a result, it becomes difficult
`to determine the cfi‘ect of various parameters on signal
`amplitude and wave-form, optimize sensor sensitivity to
`light intensity and the arrangement of the optical ele—
`ments, and hence assess the dependence of arterial oxygen
`saturation measurement on key physical, technical and
`above all physiological variables. This was the aim
`driving our decision to design, develop and construct
`in-house a system dedicated to obstetric applications.
`Following a brief review of the principles of pulse
`oximetry, we report our experience with the develop—
`ment of the new device,
`together with some field-
`testing results.
`
`The ratio between the ac and dc amplitudes is then
`
`FITBIT, Ex. 1014
`
`

`

`Kemp cl al: The Zurm'r Obsrrrrr't Rqfiermnre Pulse ()ximrrrr
`
`405
`
`l' = flC/dc = (Insure/“tissue + Itllr))'
`(502 -
`€Hbo + (l - 502) ‘ EHbl ' d-
`
`6
`
`(
`
`)
`
`this ratio r is
`In the case that “direct light” 1,“, = 0,
`independent of the incident light intensity In and of the
`absorption in the nonpulsating tissue value ltissuc:
`
`However, despite various theoretical models [9, '10],
`the scatter coefiicients of the various tissue types are
`not known with sufficient accuracy to permit exact
`calculation. Experimental calibration thus has to be
`performed by directly comparing the pulse oximeter
`readings with arterial blood sample values.
`
`r = ac/dc =
`
`(50; ' EH50 + (l — 802) ' E's-ml
`
`' (l
`
`for lair = 0.
`
`(6a)
`
`Transmission pufse oxuuetry
`
`The measured AC signals are seine 10 times weaker
`
`0 No light must be measured that has not passed
`through the pulsatile vascular bed e.g. light passing
`directly from light source to receiver (1:5,).
`I The pulsatile changes in artery thickness must be the
`same for both wavelengths,
`i.e. both wavelengths
`must transilluminate the same tissue region.
`0 Valid measurement assumes that the pulsatile signal
`originates only from varying absorption by arterial
`oxygenated and reduced hemoglobin. The results are
`falsified by other causes ofpulsatile changes in optical
`thickness, e.g. hemoglobin derivatives, circulating
`pigments, pulsatile changes in thickness produced
`mechanically in nonarterially perfused tissue by car—-
`diac action, and, above all, venous pulsation.
`To simplify description ofthe principle behind meas—
`urement and its limitations,
`the Lambert-Beer law
`
`This ratio r is then dependent only on the oxygen
`saturation 302 to be determined, the known absorption
`coefficients eHbo and 5H5, and the mean pulsatile change
`d in the thickness of the arterial vessels in the trans-
`
`illuminated region.
`To eliminate this dependence on d, the measurement
`is performed at two wavelengths with maximally dif-
`fering absorption coefficients. On the assumption that
`the d values are the same for both wavelengths, we
`obtain a variable
`
`R = I‘mi/l‘ir = (RC/dclrcd/(M/dclu
`
`(7)
`
`= (502 - sHbo + (1 c 502) ' EHb)rr—d/
`(502 ' EHho + (l — 502) ' 5Hblir
`
`7a
`
`(
`
`}
`
`from which the unknown 50; is readily calculated
`without knowing the incident light intensity or tissue
`thicknesses.
`
`Calculation assumes the following physical prerequi—
`Sites:
`
`was assumed valid for the passage of light through
`tissue. However, as light is not only absorbed in tissue
`but also scattered, the law is oflimited applicability
`[8}. The exact absorption coefficients must be cor—
`rected by taking the scattering effect into account.
`
`The optical elements are located on opposite sides ofa
`body part. The sensors are applied mainly to the fingers
`and toes. Ears and nose are used only rarely due to poor
`perfusion. ln neonates the sensor is applied around the
`hand or foot. This arrangement largely ensures that the
`optical paths are the same for both wavelengths. Never—
`theless, incorrect sensor attachment can give spurious
`results, e.g. if some of the transmitted light reaches the
`receiving diodes around the outside ofa finger as “direct
`light.”
`Signal magnitudes are an important determinant of
`measurement accuracy: in normal fingertips, the ratio
`ofthe signal due to absorption in pulsating blood (ac)
`to the signal due to absorption in total tissue (dc), r =
`acldc, is 0.02—0.05.
`
`Reflectance pulse oximetry
`
`In this method the light backseattered in the body is
`used to determine oxygen saturation. The optical ele-
`ments are thus located on the same plane on the same
`body surface. Reflection originates from nonhomo-
`geneity in the optical path, i.c. at the interfaces between
`materials with different refractive indices. This means
`
`that on physiological grounds, strong reflections can be
`expected on the entry of light into bone. The trans-
`illuminated tissue must also be well perfused to obtain
`as strong a signal as possible. Not all body parts are as
`well perfused as the fingers or hands, but an acldc ratio
`of 0.001e0.005 can be achieved on the forehead. Perfu—
`sion is also good over the sternum. One method of
`signal enhancement is to heat the measurement site to
`induce hyper-perfusion, which can safely be performed
`up to 42°C. A rubefacient, e.g. nicotinic acid (Rubri-
`ment). can also be applied to the measurement site.
`The principal physical limitations are the following:
`
`The sensor design must eliminate “direct light,” i.c.
`light passing directly from the light sources to the
`photodiodes or that is only scattered in the outer part
`of the skin.
`
`FITBIT, Ex. 1014
`
`

`

`406 Journal ofCliniml Monitoring and Computing Val 14 Na 6 August 1998
`
`than in the transmission method. The conditions
`
`governing the heating of the light—emitting diodes
`(LED) limit
`the potential for producing stronger
`signals by increasing the incident light intensity: not
`only can high uncontrolled temperatures damage
`tissue at the measurement site, but the wavelength
`of the emitted light changes as the LEDs become
`warmer. For this reason the photodiode area must be
`as large as possible.
`As in the transmission mode, the principle of meas—
`urement is the determination of absorption. except
`that this now refers to incoming reflected light. The
`light path is less well defined than in transmission
`mode, and thus may differ between the two wave—
`lengths. The effective absorption coeflicients of the
`calibration inserted in the Lambert—Beer law must be
`
`checked and if necessary corrected by comparison
`with photometrically measured arterial blood values.
`
`neonatal head. Experimentation led to the choice ofa
`vacuum system using sensors cast from silicone rub—
`ber, with a suction groove for fixation, a guard ring
`against direct light, and a connector for a suction
`pump. The photoelectric components are identical in
`both types of sensor.
`I Some metal sensors were fitted with a resistance-wire
`
`heating coil of maximal output 200 mW to induce
`local hyperemia. The temperature was monitored by
`a negative temperature coefficient (NTC) resistor in-
`corporated in the sensor unit.
`
`Numerous types of sensor meeting the above require-
`ments were built. A sensor used for intrapartum meas-
`urements — cast from silicone rubber with suction
`
`channel and pump connection — is shown in cross-
`scction in Figure 1. It is attached to the fetal head with a '
`vacuum of approximately 100 mbar.
`
`TIIE lelllllH IIEFLEBTANEE PIILSE lllllllETEB
`
`Electronics
`
`the 1 kHz sampling rate in the equally spaced se—
`
`o For maximal independence from local tissue differ—
`ences, a radially—symmetric pattern was selected for
`the photoelements. The light source e a chip with
`two LEDS for the wavelengths red = 660 nm and
`infrared : 920 nm A was placed in the center of the
`sensor and surrounded by a radial photodiode array
`for detecting the reflected light. To obtain a good
`signal at minimal
`light intensity,
`the area of the
`photodiodes had to be as large as possible. After some
`preliminary experiments,
`six BX33 photodiodes
`(Siemens) were used with a mean radius of ‘17 mm.
`Their connections are led outwards individually, so
`that the sensor as a whole remains operational if a
`wire breaks or an individual diode is lost. This arrange-
`ment gives an external sensor diameter of 22 mm.
`A guard ring around the LEDs acts as a barrier to
`"direct light." The sensor must also fit snugly to the
`skin to minimize the risk of ambient light reaching
`the photodiodcs.
`Unlike with transmission sensors, fixation to the
`measurement site can pose problems. Aluminum sen—
`sor units are readily fixed with double-sided adhesive
`ECG rings. However,
`these rigid sensor heads are
`unsuited to the small radii of curvature of the fetal]
`
`Sensors
`
`In constructing planar reflection sensors, i.e. sensors in
`which the photoelectric emitting and receiving elements
`lie next to each other in virtually the same plane, special
`attention was paid to the following points (Figure 1).
`
`Initially, we decided to separate signal processing in the
`analog part before the analogfdigital converter (ADC).
`including signal amplification, filtering. and separation
`into DC and AC signals, all handled electronically ; the
`post-ADC digital part was handled by software which
`input the data, averaged and evaluated amplitudes, cal—
`culated saturation and heart rate, and produced a some—
`what complicated sereen display. Now, using modern
`techniques, we have a system in preparation in which a
`fast separate microprocessor unit handles most signal
`processing and digital filtering tasks.
`Figure 2 shows the block diagram of the current
`apparatus with the following individual units:
`
`I Time control of measurement
`
`From a rectified mains power supply signal (100 Hz),
`a phase—locked loop (I’LL) — connected as a frequency
`multiplier — generates a square—wave signal of 64
`kHz. Coupling to the line frequency eliminates data
`acquisition faults due to interferences with the line
`frequency. The 64 kHz from the PLL clock drives a
`' 7-bit counter that addresses an EPROM giving a data
`Cycle of] kHz, 64 pulses long. The output pulses of
`the EPROM control
`the entire sequence of light
`emission, signal acquisition and signal processing.
`LED drive
`
`The oppositely poled red and infrared LEDs are
`located in the output circuit of a current-stabilized
`push—pull output stage. They are triggered by digital
`signals from the control unit via analog switches at
`
`FITBIT, Ex. 1014
`
`

`

`Kc'imlg N m': Thr Zurt'rh Obslrrrir Rqflermmr Prdn- er'mz'fc’."
`
`407
`
`Fig. 1‘ Cress-senior: “trough a silirnnu- rrrhbm' rqflccrfon scusorfor immpm'mm mcasmwneur {fox}!ch saturation.
`
`(D Photodiodes
`C2)
`Red and Infrared LED's
`6)
`Light barrier
`
`FITBIT, Ex. 1014
`
`

`

`408 junrrmquCl'iniml Monitoring and Computing V0114 No6 August 1998
`
`Vacuum
`Pump
`and
`Control
`
`P“?
`Amplifier
`
`Computer
`
`producing a maximal —300 nibar vacuum. The pump
`
`quence: infrared-dark—red—dark (overall length: 1 m5).
`Light intensity is determined by the amplitude of the
`signal driving this output stage. Input signal intensity
`can be selected in two ways:
`4 Manually; The red and infrared LED intensities
`can be manually adjusted independently using two
`potentiometers (Helipot). This permits the use of
`any desired light intensity within the limits stipu-
`lated for test and research purposes.
`Automatically: DC voltage as the input signal
`controls the LEDs so that the DC voltages at the
`computer input for both wavelengths are 2.0 :i: 0.5
`V. Outside this range the control circuit changes
`the LED currents to reset the DC voltages to 2.0 V.
`This setting is used for normal clinical applications.
`To prevent skin damage from overheating even in
`the event of electronic component failure, maximal
`LED intensity is limited by an electronic circuit.
`Input amplifier and sample—and—hold stages
`Using operational amplifiers the photocurrent sup-
`plied by the photodiodes is converted toa voltage
`and then amplified. Six switch positions permit am-
`plifications of 50 menA to 5 V/nA. Afterwards,
`three sample—and—hold (8&H)
`stages — switched
`by the corresponding signals from the control stage -
`resolve the signals into the three components infra—
`red, red and dark. The dark currents are then sub—
`tracted from the red and infrared signals in a subtrac—
`tion stage which also eliminates small ambient light
`components that may have reached the photodiodes.
`
`OscillatorfControl Unit
`
`Ext. Device
`
`(HP, Nellcor)
`
`Fig. 2. Schematic representation qucasuremem electronics.
`
`u Filters
`
`Using low-pass filters the discrete—time signals at the
`8&1-1 output are reconverred to continuous—time sig-
`nals and trimmed of high—frequency components
`using eighth-order Bessel
`filters with a cut—off
`frequency of 7 Hz. The DC components are then
`separated using a low-pass filter with a cut-off fre—
`quency of0.1 Hz. The AC components are passed to a
`further Bessel high-pass 0.7 Hz filter for separation of
`slow motion artifacts, and then to a 40—fold amplifi-
`cation stage. The four signals DC”, DCrcd, AG, and
`ACRE. are thus available at the output. As oxygen
`saturation is calculated from the ratios (acjdch, and
`(acfdc)rcd, it was essential to ensure by careful com—
`ponent selection that the amplifications for the am~
`plification and separation stages were as near as possi—
`ble identical for both wavelengths.
`Patient insulation
`
`the LED controller output
`For patient protection,
`stage and photodiode input stage were electrically
`'isolated from the mains using Burr 8: Brown isola-
`tion amplifiers. These units were powered by an
`insulated power pack.
`Heating
`Sensors incorporating a resistance coil were fitted with
`a precision controller stabilizing temperature within
`the range 38.0—41.0 °C to an accuracy of0.] °C.
`Vacuum pump
`The sensor is fixed to the skin using a small pump
`
`FITBIT, Ex. 1014
`
`

`

`Kiiflig M iii: The Zurich Obstetric Reflerram'e Pulse Oximcrer 409
`
`Start: 33. 1.9? 8:19:21 Tot.TiHa: 60 Min
`RFDXLJ.
`Lxxxxxxx Rxxx geh. 20.03.63 US Datum 23.01.97
`
`0 sec File: LRDBl922.PX2
`"Fox
`802 y
`
`|||||||||||||||||l||||
`
`CTG HR bun
`
`|l|l|
`
`IIIIaIIIIIs
`
`12
`
`—_ _—_E
`
`.1
`
`law is limited by scattering in tissue, experimental
`
`(ADC) card (Mctrabyte). A counter on this card
`triggers analogfdigital conversion at 400 Hz, which
`starts an interrupt program in the computer for read-
`ing the 4 measured values DC,“ DCm; and AC,“
`Acred into a cyclic buffer of 5-seconcl length. From
`the signal (AC5.-+AC,cd) the maxima and minima are
`determined for each cardiac cycle, and hence the
`instantaneous heart rate. Oxygen saturations are cal-
`culated from the amplitudes ac and dc of the AC and
`DC signals.
`Saturation is calculated from the Lambert-Beer
`
`Marker: n
`
`Fig. 3. Street! display of a 10-minute measurement. From top to bottom: oxygen saturation, heart rate, hear: rarefrum HP CTG monitor,
`uterine cairrracriaiifi'om HP CTC monitor. Underneath the DC and AC signals for iiy‘imed and red liglitfor the last 5 seconds (More the
`different ordinate Sfal'csfor DC and AC).
`
`is maintained electronically via a manometer at a
`preset negative pressure. In normal medical use, ad-
`equate fixation is achieved with a vacuum of about
`—l00 mbar.
`
`Sqflware
`
`Apart from various test programs, a program for data
`acquisition, display, calculation and storage and a pro-
`gram for subsequent data postproeessing were written
`in PASCAL.
`
`0 Signal acquisition, calculation and display
`For data acquisition a 486 DOS computer was
`equipped with a 12—bit analogfdigital conversion
`
`the
`for
`law using the absorption coefficients [11]
`nominal wavelengths of our LEDs. However, as
`the actual wavelengths may deviate from these nom—
`inal values and the applicability of the Lambert-Beer
`
`FITBIT, Ex. 1014
`
`

`

`410 journal quiiniml Monitoring and Ceiiipiriing Voi14 No 6 August 1998
`
`calibration ofthe measured saturation values is essen-
`tial.
`
`Calibration
`
`Saturation and heart rate can be averaged over 1—9
`cardiac cycles and are displayed every second. Analog
`heart rate and uterine contraction signals from any
`CTG monitor With analog output
`(e.g. Hewlett
`Packard model 8040) can be input to the ADC every
`second and likewise displayed.
`The measurement display (Figure 3) shows, along the
`bottom, the 4 measured values DC,“ DCmd and ACi“
`ACrcd, over the last 5 seconds of measurement. This
`serves to monitor signal quality during acquisition.
`Poor—sign a1 periods can be marked and excluded from
`data processing. Along the top, measured arterial
`oxygen saturation and heart rate values per second are
`displayed cyclically over a 10-minute interval, with
`the CTG heart rate and contraction input under-
`neath. Any time point can be marked for subsequent
`identification and all values and comment stored in a
`
`file at any time.
`Data analysis
`The values from a stored file can be redisplayed in
`measurement mode using an evaluation program.
`Time intervals can be marked with the arrow keys or
`mouse. Means and standard deviations — including
`the CTG data # are then calculated and displayed.
`
`
`
`HEASIIIIEHIEHTS Mil IIISEIJSSIIIN
`
`Clinical application of any new instrument or measure-
`Inent system presumes:
`
`Approximately 100 what is the most suitable pressure
`
`7 mechanical reliability, accuracy and calibration,
`— feasibility in the clinical situation, including accept—
`ance by both medical personnel and patients,
`the ability not only to determine physiological pa-
`rameters not previously measured in both physiolog—
`ical and pathological situations, but also to evaluate
`the diagnostic significance of such parameters, in this
`case oxygen saturation.
`For the first two more technical points is to say, that
`our instrument required calibration before clinical
`use, together with field tests ofthe suction device and
`long—term oximeter performance during birth.
`For
`these points controls and clinical
`trials were
`performed in our own unit and with colleagues in
`Copenhagen (DK), Graz (A), Oulu (SF) and Berlin
`{D}. The major investigations comprised:
`
`To calibrate a pulse oximeter, an oxygen saturation
`value must be assigned to the measured variables
`
`R =
`
`: (adders/(acacia
`
`cf {7)
`
`on the basis of an experimental or theoretical relation-
`ship. Initially we used the absorption coefficients of
`Zijlstra e1 (ii [1 l]. The general problems of calibrating a
`pulse oximeter have been discussed elsewhere [12, 13].
`For fine calibration we performed the following inves-
`tigations:
`
`o Tests in the arterial oxygen saturation range 88—
`lOO% were conducted in 14 healthy adult volunteers
`breathing normal air and then air with approxi-'
`mater 80% normal oxygen content for 10 minutes
`in each case. The reflection sensor was fixed to the
`
`forehead or sternum with an adhesive ring. Owing to
`the invasive nature of arterial catheterization. refer~
`
`ence values were provided by a MINOLTA PUL-
`SOX 8 transmission pulse oximeter attached to the
`index finger. Data analysis [13] showed a 4.5% differ-
`ence in oxygen saturation between the MINOLTA
`and the preliminary results of our reflectance system
`based on the absorption coefiicents onisztra et a].
`At lower saturation levels, measurements were per—
`formed in cyanotie children before surgery. The chil—
`dren had arterial lines, permitting direct comparison
`with arterial bleed readings [14].
`Low saturations in viva can also be measured in the
`
`fetal lamb [15]. We used this method to compare our
`pulse oximeter readings directly with arterial values
`in the oxygen saturation range 10—80% [16].
`
`Preliminary evaluation of these data shows that our
`previous calculations of oxygen saturation have to be
`corrected in the ill—100% saturation range by a factor of
`1.045.
`
`Fixation
`
`The first experiments in sensor fixation to the head and
`other parts of the human body were performed in
`adults [17] and neonates [18].
`Attachment is simple in practice, even during birth.
`After rupture ofthe membranes, the sensor can be fixed
`to the fetal head once the cervix has dilated to at least 2
`cm. Initial fixation takes 30—60 seconds and allows full
`
`freedom ofmovement [19].
`
`FITBIT, Ex. 1014
`
`

`

`. johnson NJohnson VA, Fishcerobbings B, Bannister].
`Lilford R]. Feta] monitoring with pulse oxinietry. Br]
`Obstet Gynaecol 1991; 98: 36—41
`. Knitza R,Buschmann], Rall G. Ein neues Verfahren zut
`kontinuierlichen Messuug der Fetalem Sauerstofl‘séitti-
`gong sub patru. Geburts Frauenheilk 1992; 52: 319—321
`. Dildy GA, Clark SL, Loucks CA. Preliminary experience
`with intrapartnm fetal pulse oxiinetry in humans. Obstet
`Gynecol 1993; 81: 630—635
`. Hypoxische Gef‘a'hrdung des Fetus sub partu. ln: Knitza
`R (ed). Darinstadt: Steinkopf1994
`. Wukitsch MW, I’etterson MT, Tobler DR, PologeJA.
`Pulse oxi merry: Analysis of theory, technology and prac—
`tice.j Clin Monit1988;4: 290—301
`. Graaff R. Tissue optics applied to reflectan